This invention relates to an apparatus and a method for checking value documents, in particular bank notes, and a value-document processing system.
In bank-note processing systems, properties of bank notes, such as e.g. printed image, denomination, authenticity and condition, are ascertained by capturing physical properties of the bank notes by means of sensors and evaluating the thereby generated sensor data.
For checking the bank notes, their remission and/or transmission properties are often utilized. For this purpose, respectively one bank note is irradiated with the light of one or several light sources and the light remitted, i.e. diffusely reflected, or transmitted by the bank note is captured by means of one or several sensors. Depending on the kind of light sources used, the remission or transmission curves ascertained in this way may deviate from the actual remission or transmission behavior of the bank note. For example, when light-emitting diodes (LEDs) are used as light sources, artifacts may occur in particular regions of the remission or transmission curves, which do not correspond to the actual properties of the bank note.